1. Field of the Invention
The invention is directed to magnetic bubble domain memory devices, in general, and to magnetic bubble domain memories using an integrated buffer memory, in particular.
2. Prior Art
Buffer memories are used in computer memory hierarchy to improve the flow of data between the mass storage memory and the main memory of the computer. That is, it has been observed that a block of data is likely to be called again shortly after it has been called once before. By retaining the most recently called bocks of data in a buffer memory, the average data flow rate is greatly increased inasmuch as the buffer acts in a time which is much shorter than that of the mass memory. A mass memory is usually of the magnetic recording tape such as discs, drums and the like. On the other hand, the buffer includes memories of the semiconductor or magnetic core type memories.
Magnetic bubble domain technology, which is a contender for the mass memory application, unlike the magnetic recording technology, is very flexible in the way the data can be manipulated within the bubble chips. Bubble domains can be switched between different storage tracks and data reordering or reallocation can be readily achieved. These features make it possible to construct a bubble memory with different levels of capacity and access time. In other words, an integrated memory hierarchy can be achieved using magnetic bubble domain technology.
Several methods have been proposed to achieve data reallocation within the bubble chip. One such version is described by C. Tung et al in "Bubble Ladder for Information Processing", IEEE Transaction on Magnetics, Vol. Mag.-11, No. 5, September 1975, P.463. In this version, there is utilized what is called a "Bubble Ladder" which is composed of a large storage loop which can be selectively divided into two or more sub-loops by using crossover switches. Thus, data reallocation can be achieved by properly controlling the operation of the switches relative to the information in the loop.
Also, Bonyhard et al, "Dynamic Data Reallocation in Bubble Memories", BSTJ, Vol. 52, page 307 (1973), describes the use of a new circuit configuration. In this latter version, a bit (bubble) can be inserted or removed without leaving a gap in the storage loop as a function of the direction of the field sense of rotation. Bubble permutation and, thus, reallocation of data can thus be performed.
U.S. Pat. No. 3,701,132, Dynamic Reallocation of Information on Serial Storage Arrangements, Bonyhard et al, further describes a bubble domain mass memory of the major/minor loop configuration which is adapted for the reordering of stored information depending upon the recent use of the information.
Other methods of rearranging or reallocating bubble domain information in storage loops are known. However, alternative methods of reallocating bubble domain information to permit improved operation of the memory are desirable. In addition, it is desirable to provide circuit components which enhance the performance of this type of apparatus.